A 52-year-old man presents with acute onset of severe eye pain, blurred vision, and a fixed, mid-dilated pupil. Anterior chamber examination shows corneal edema and elevated intraocular pressure (68 mmHg). Gonioscopy reveals angle closure. What is the drug of choice for immediate management of the acute attack?

Explanation

## Acute Angle-Closure Glaucoma: Pharmacological Management ### Clinical Context Acute angle-closure glaucoma (AACG) is an ophthalmic emergency characterized by sudden elevation of intraocular pressure (IOP) due to pupillary block mechanism. The mid-dilated, fixed pupil and corneal edema are classic findings. ### Drug of Choice: Pilocarpine **Key Point:** Pilocarpine is a muscarinic agonist (direct-acting parasympathomimetic) that causes miosis (pupil constriction) and ciliary muscle contraction, thereby pulling the iris away from the angle and relieving pupillary block. **High-Yield:** In acute angle-closure glaucoma, pilocarpine works through two mechanisms: 1. **Miosis** — constricts the pupil, relieving the mechanical block 2. **Ciliary muscle contraction** — deepens the anterior chamber and opens the drainage angle ### Mechanism of Action - Binds to muscarinic M3 receptors on the iris sphincter and ciliary muscle - Causes sustained pupillary constriction - Improves aqueous humor drainage via trabecular meshwork ### Dosing in Acute AACG - **Topical:** 1% pilocarpine solution, 1 drop every 5–15 minutes for 1–2 hours, then every 4–6 hours - **Systemic adjuncts:** IV acetazolamide (500 mg) + IV mannitol (1 g/kg) to lower IOP rapidly before pilocarpine takes effect ### Clinical Pearl **Timing is critical:** Pilocarpine is most effective when IOP is <40 mmHg. At very high pressures (>60 mmHg), the iris becomes ischemic and unresponsive to pilocarpine — in such cases, systemic agents (acetazolamide, mannitol) must be given first to lower IOP sufficiently for pilocarpine to work. ### Definitive Treatment Once the acute attack is controlled, **laser peripheral iridotomy** or **surgical iridectomy** is performed to prevent recurrence by eliminating the pupillary block mechanism. ### Comparison Table: Pupil-Acting Drugs in Glaucoma | Drug | Class | Effect on Pupil | Effect on IOP | Use in AACG | | --- | --- | --- | --- | --- | | **Pilocarpine** | Muscarinic agonist | Miosis | ↓ (via angle opening) | **First-line** | | Tropicamide | Muscarinic antagonist | Mydriasis | ↑ (worsens block) | **Contraindicated** | | Phenylephrine | α1-adrenergic agonist | Mydriasis | ↑ (worsens block) | **Contraindicated** | | Atropine | Muscarinic antagonist | Mydriasis (prolonged) | ↑ (worsens block) | **Contraindicated** | **Warning:** Anticholinergics (atropine, tropicamide) and sympathomimetics (phenylephrine) cause mydriasis and worsen pupillary block — they are absolutely contraindicated in acute angle-closure glaucoma.